Carbon nanofibers are rapidly emerging as multifunctional reinforcement material for composite applications because of their potential for high strength, high elastic modulus, high thermal and electrical conductivity, and low density. Potential applications concern aerospace, automotive, bio-medical, and sporting goods in the form of structural laminate and woven composites to improve matrix toughening.
Carbon fibers can be produced by vapor deposition or from organic precursor nanofibers, such as polyacrylonitrile (PAN) and pitch. Microscale pitch-based carbon fibers have a high modulus and good thermal and electrical conductivities and are thus suitable for a variety of applications. On the other hand, PAN has become the predominant precursor for carbon fiber production due to its high yield and the flexibility of tailoring strength and modulus based on the carbonization and graphitization temperatures. Carbon fibers based on PAN precursors typically have diameters in the range of 5-10 microns.
Attempts to produce PAN-based carbon fibers having nanoscale diameters have met with limited success to date, as the resulting carbon nanofibers are not competitive with micron-scale PAN-derived carbon fibers in terms of mechanical properties.